Saudi oil men grapple with; RUST
Dhahran, Saudi Arabia — Oil technicians here are grappling with a multimillion-dollar problem -- rust. Since the late 1930s pipelines and other production hardware have spread across the barren Eastern Province like a steel web. In 1979 alone more than 500 miles of pipeline, ranging in diameter from 3 inches to 48 inches, were completed or under construction.
Now that vast network, which carries nearly one-fifth of the noncommunist world's oil supply, has to be protected by what is said to be one of the world's largest corrosion control teams. without this special care, engineers estimate that oxygen, carbon dioxide, and water corrosion could eat into the pipe walls at rates as rapid as an inch a year.
Some 50 engineers and workers in Dhahran, supported by up to 100 maintenance men in the corrosion control department, coordinate the tasks of making the Arabian American Oil Company's (Aramco) hardware last as long as possible.
While it now costs less than $1 to produce a single barrel of $32 Saudi crude , production and maintenance costs are increasing. The increase is not in proportion with skyrocketing oil prices in recent years, but the investment for Aramco in money and expertise is significant. Most of the cost increases are due to the difficulties of maintaining high production levels in aging oil fields and producing oil in more remote areas. Corrosion control makes up but a small part of this total maintenance effort.
To combat this natural process, the department packs an arsenal of paints and coatings, corrosion reducing metals, and chemicals such as bactericides and oxygen scavengers.
"Corrosion control is more an art than a science," says an Aramco engineer. Experts must determine which of some 25 to 30 different corrosive mechanisms are at work and the most economic methods available to retard them. Such determinations are often difficult when the reactions are occurring, for instance, in an underground bend in a long producing pipeline or deep in an oil well.
In recent years the experts have to battle a new problem -- bacterial infections. The bacteria, which plague oil companies around the world, were not a problem here until three or four years ago -- after the company began a program of injecting water into the oil fields to maintain production pressure.
Some specialists feel the process may have triggered the incubation of an ever-accelerating bacteria population. Since that population grows increasingly immune to poisonous chemicals, poison is injected at three-month intervals to allow a bacteria colony to build up moderately while reducing its exposure to the bactericide, thus discouraging the development of an immunity.
The corrosive bacteria come in two basic classes. One converts noncorrosive sulfate into highly corrosive hydrogen sulfide. The other produces substances that disrupt the electron equilibrium among the elements in steel, causing what is termed "cathodic depolarization."
Basic corrosives other than bacteria include carbon dioxide, which will form a weak bubbling acid like soda pop when under pressure in water solution, and oxygen, a primary agent in corrosion. Chemical scale inhibitors are applied to reduce the acidity of water solutions with a high concentration of carbon dioxide.
In addition to chemicals to kill bacteria, reduce acidity, and eliminate oxygen, Aramco uses chemicals called corrosion inhibitors, which are injected into the producing system (pipes and production hardware such as pumps) with any mixture of the other chemical treatments. Corrosion inhibitors cling to pipeline and system interiors, forming a protective shield between the pipeline and the material running through it and any corrosives contained within.
Currently, Aramco's largest single corrosion problem is in the water-injection facilities in the southern oil fields (the world's largest known concentration of oil) where carbon dioxide and water -- under pressure of 50 to 60 pounds per square inch -- mix with oxygen.
"We've seen water pipelines, which simply couldn't control the oxygen influx, turn into a sprinkler system in three years," an engineer said. To avoid that kind of rapid breakdown, technicians use chemical oxygen scavengers that tie up the oxygen chemically, making it unavailable to interact with other agents.
A typical application of a chemical treatment in an area where water injection is being used involves squeezing perhaps twenty 55-gallon drums of chemical mixture into a pocket of ground water slated for injection into an oil-bearing rock formation. Technicians then hope to find a concentration of at least five parts per million of the chemicals flowing back through the systems during a three-month period.
Another -- and highly successful -- method of using chemical treatments includes the introduction of a slug of bactericide and corrosion inhibitor into a pipeline between two buoyant plastic scrapers. The scrapers, which fit inside the pipe and are pushed by the flow, plow the bacteria and other foreign materials out of the line while the bactericide kills any remaining bacteria.
The alternatives -- painting or coating existing facilities or reconstructing large portions of the system with more corrosion-resistant alloys -- are far more costly.
"We are faced with a situation where we really have no other alternatives," an engineer said. He added that a promising technology using protective coating is advancing. But even if a cheap alternative were announced today, it would probably not be applicable to the thousands of miles of existing pipelines extending through the Saudi desert.
In addition, technicians say it is rare to find a single corrosive mechanism working in isolation. It is more common, they say, to find three or four processes under way, which complicates efforts to determine the contribution of each corrosive process to the total damage.